This invention generally relates to an intravascular catheter for ablating tissue of a patient's heart and particularly to an ablation catheter which can be advanced through the patient's coronary arteries or cardiac veins to treat arrhythmia from within the blood vessel.
Prior methods for treating a patient's arrhythmia include the use of antiarrhythmic drugs such as sodium and calcium channel blockers or drugs which reduce the Beta-adrenergic activity. Other prior methods include surgically sectioning the origin of the signals causing the arrhythmia or the conducting pathway for such signals. More frequently, however, to terminate the arrhythmia the heart tissue which causes the arrhythmia is destroyed by heat, e.g. applying a laser beam or high frequency electrical energy (RF or microwave) to a desired location on the patient's endocardium.
In the latter instance, the location of the tissue site causing or involved with the arrhythmia must be accurately know in order to e able to contact the desired location with a tissue destroying device. A major problem with ablating the site of the origin of the signals or a conductive pathway is to accurately determine the location of the site so that an excessive amount of healthy tissue is not damaged or destroyed along with the arrhythmogenic site, while at the same time ensuring that the arrhythmia does not return. For example, the average arrhythmogenic site consists of an area of about 1.4 cm.sup.2 of the endocardial tissue, whereas a re-entrant site might be much larger. RF ablation techniques produce lesions about 0.5 cm.sup.2 in area, so several lesions may be necessary to completely ablate an area of interest. If the arrhythmogenic or reentrant site is not accurately mapped, much healthy tissue surrounding the site will be unnecessarily damaged or destroyed.
A variety of prior methods have been used to detect electrical activity within a patient's heart to facilitate the mapping of electrical activity causing the arrhythmia. A number of these prior methods are disclosed in U.S. Patents which use elongated intravascular signal sensing devices with one or more electrodes on a distal portion of the device which are advanced through the patient's vasculature until the distal portions of the sensing devices are disposed within one or more of the patient's heart chambers with one or more electrodes in contact with the endocardial lining. While this procedure is widely used, it does not always allow the site of the arrhythmogenic signals to be accurately determined.
In U.S. Pat. No. 5,509,411 (Littmann et al.) which issued on Apr. 23, 1996, reference is made to intravascular devices which are advanced through a patient's coronary arteries or cardiac veins to desired locations in the patient's epicardium where electrical activity is detected by means of electrodes on the distal ends of the devices to locate arrhythmogenic sites or conductive pathways causing or involved with the arrhythmia. In copending application Ser. No. 08/207,918, filed Mar. 8, 1994 an intravascular device is described which uses RF energy to occlude a blood vessel in order to destroy tissue distal to the catheter by creating ischemic conditions therein.
While these prior devices provided many advantages, there were no ways of controlling the temperatures of the emitting electrodes.